High performance insulation is generally characterized by relatively low density because higher densities generally result in poorer heat transfer resistance characteristics due to easier thermal conduction through the denser medium. As a result of this relatively low density, high performance insulation has poor compressive strength and cannot support a significant load. When high performance insulation is required in a load bearing application there is sometimes employed one or more pegs of adequate compressive strength interspersed throughout the insulation to support the load.
Several such load bearing pegs are known to the art. For example, U.S. Pat. No. 3,094,071--Beckman teaches the use of spacers made of porcelain or organic thermal-setting plastic reinforced with fabric or paper. U.S. Pat. No. 3,289,423--Berner teaches the use of pegs of glass fibers made by giving together layers of glass fibers. U.S. Pat. No. 3,161,265--Matsch discloses pegs of glass reinforced phenolic resin and suggests ceramic pegs for high temperature uses.
Although such known pegs are adequate for many uses, they are inadequate for certain high temperature high performance applications. As can be appreciated, thermal transfer through a peg is considerably greater than through the low density insulations. In certain high performance applications the thermal transfer through the pegs is so high as to defeat the purpose of the low density high performance insulation. One such high performance application is an evacuated enclosure for a high temperature battery such as might be used to power an electric vehicle.
Specifically, high density pegs such as those made of porcelain or other ceramics have the disadvantage of relatively high thermal conductivity at elevated temperatures. To reduce such heat transfer, the peg support area must remain small thereby compromising the load bearing capability of the peg. Pegs containing binders, resins or similar reinforcers provide a continuous non-insulator conductive heat path, thus significantly increasing heat transfer through the peg. Furthermore such binders and resins may give off vapors at elevated temperatures which would degrade the vacuum in applications where evacuation of the insulated volume is employed. Such vacuum degradation further reduces the degree of insulation achievable.
It can be appreciated that a successful load bearing insulation peg must have both compressive strength and insulating capability. However those qualities which impart to a peg compressive strength, such as density and reinforcers, also tend to decrease a peg's insulating capability.
It is therefore an object of this invention to provide an improved loading bearing insulation peg.
It is another object of this invention to provide an improved load bearing insulation peg of relatively high density and compressive strength.
It is further object of this invention to provided an improved load bearing insulation peg of relatively high density and compressive strength which has improved thermal resistance characteristics than heretofore available pegs having comparable compressive strength.